Antimicrobial peptide gene BdPho responds to peptidoglycan infection and mating stimulation in oriental fruit fly, Bactrocera dorsalis (Hendel).

Phormicins belong to defensin family, which are important antimicrobial peptides (AMPs) in insects. These AMPs are inducible upon challenging by immune triggers. In the present study, we identified the cDNA of a phormicin gene (BdPho) in the oriental fruit fly, Bactrocera dorsalis (Hendel), a ruinous agricultural pest causing great economic losses to fruits and vegetables. The cDNA of BdPho contains a 282 bp open reading frame encoding 93 amino acid residues, and the predicted molecular weight and isoelectric point of BdPho peptide were 9.83 kDa and 7.54, respectively. Quantitative real-time PCR analyses showed that the transcription level of BdPho was the highest in adult during different developmental stages and was the highest in abdomen among adult tagmata. Moreover, BdPho was highly expressed in fat body among different tissues, both in female and male adult. The mRNA level of BdPho was significantly up-regulated to 7.46- and 14.53-fold at 3 and 6 h after the insects were challenged with peptidoglycans from Escherichia coli (PGN-EB), respectively, suggesting its antimicrobial activity against Gram-negative microorganisms. Furthermore, the expression level of BdPho was significantly up-regulated to 3.83-fold after mating, suggesting that female adults might enhance their immunity by up-regulating the expression level of BdPho during mating. These results firstly describe the basic properties of the phormicin gene from B. dorsalis, and lay the foundation for investigating functional properties of AMPs and exploring the molecular mechanisms in the immune system.